Add power-on/off G-code options (#19837)

Co-authored-by: Chris <chris@chrisnovoa.com>

Marlin/Configuration.h

   //#define PSU_DEFAULT_OFF         // Keep power off until enabled directly with M80
   //#define PSU_POWERUP_DELAY 250   // (ms) Delay for the PSU to warm up to full power
 
+  //#define PSU_POWERUP_GCODE  "M355 S1"  // G-code to run after power-on (e.g., case light on)
+  //#define PSU_POWEROFF_GCODE "M355 S0"  // G-code to run before power-off (e.g., case light off)
+
   //#define AUTO_POWER_CONTROL      // Enable automatic control of the PS_ON pin
   #if ENABLED(AUTO_POWER_CONTROL)
     #define AUTO_POWER_FANS         // Turn on PSU if fans need power

Marlin/src/feature/power.cpp

 #include "../module/stepper/indirection.h"
 #include "../MarlinCore.h"
 
+#if defined(PSU_POWERUP_GCODE) || defined(PSU_POWEROFF_GCODE)
+  #include "../gcode/gcode.h"
+#endif
+
 #if BOTH(USE_CONTROLLER_FAN, AUTO_POWER_CONTROLLERFAN)
   #include "controllerfan.h"
 #endif
     safe_delay(PSU_POWERUP_DELAY);
     restore_stepper_drivers();
     TERN_(HAS_TRINAMIC_CONFIG, safe_delay(PSU_POWERUP_DELAY));
+    #ifdef PSU_POWERUP_GCODE
+      GcodeSuite::process_subcommands_now_P(PSTR(PSU_POWERUP_GCODE));
+    #endif
   }
 }
 
 void Power::power_off() {
-  if (powersupply_on) PSU_PIN_OFF();
+  if (powersupply_on) {
+    #ifdef PSU_POWEROFF_GCODE
+      GcodeSuite::process_subcommands_now_P(PSTR(PSU_POWEROFF_GCODE));
+    #endif
+  	PSU_PIN_OFF();
+  }
 }
 
 #endif // AUTO_POWER_CONTROL